This invention relates to a method and apparatus for the forming of components of complex shape, in particular turbomachine rotor wheels, which constitute a single piece with the blading, by electrochemical material removal.
As is known, the complex, three-dimensionally curved contours of blades of one-piece rotor wheels for fans, compressors and turbines made from a solid, for example the blisk-technology rotor wheels of jet engines, are produced by milling the solid with a cutting tool. Due to the heavy curvature of these blades and the complex shape of the space between the blades, the geometries of these blades are unsuitable for production in flank contact. The only way to produce these shapes is machining in point contact. However, this method is extremely cost and time-consuming and, therefore, lends itself only to a limited extent to the series-production of, for example, compressor disks in blisk technology. In addition, the surfaces are textured by the point-contact milling process and must, therefore, be ground after milling in a subsequent operation.
Also, the repair of a rotor wheel, where damaged blades or blade sections are to be replaced or corrected by mold welding, build-up welding or the like, requires costly re-machining of the item under repair by a cutting process.
A generally known forming process by material removal, as described in Specification DE 29 03 873 for example, is based on the electrochemical machining of the workpiece, with a suitably shaped electrode oscillating linearly shortly above the electrolyte-wetted workpiece surface and removing material conformally with the shape of the electrode as the latter is transversed linearly. Electrochemical material removal is effected in the so-called ECM (electrochemical machining) and PEM (precise electrochemical machining) processes such that a voltage pulse is applied to the linearly oscillating electrode when its distance to the electrolyte-wetted workpiece is minimum. The more advanced PEM process, which is free from electrode wear and thermal affection of the workpiece, is characterized by high machining precision and surface finish.
Specification U.S. Pat. No. 4,999,093 already proposed the use of the apparently advantageous electrochemical forming for the manufacture of turbine blades or other components with three-dimensionally curved contour. The apparatus described therein is, however, unsuitable for the production of one-piece rotor wheels where the blades are machined from a solid, for example blisk-technology rotor wheels, since it does not provide for the complex, three-dimensionally curved contour of the space to be produced between adjacent blades.